Defect control and measurements have been identified recently as the most significant challenges facing the implementation of III-V materials in complementary metal-oxide-semiconductor (CMOS) devices. Defects form in III-V films grown epitaxially on silicon due to fundamental mismatches at a basic material level, in particular thermal, structural, and lattice constant mismatch. Various techniques have been proposed for inspection of III-V films and other such types of materials. Specific examples of inspection techniques include bright-field transmission electron microscopy (TEM), X-ray diffraction (XRD), electron channeling contrast imaging (ECCI), and cathodoluminescence (CL). However, these techniques are often too expensive and/or time consuming and cannot be utilize in production environment.
Specifically, bright-field TEM provides an accurate determination of the dislocation density when the dislocations can be clearly distinguished. In other words, it can be applied with high accuracy below a certain dislocation density. However, the TEM inspection is destructive and time consuming and requires very demanding sample preparation. XRD provides an average dislocation density of the bulk deformed material in a shorter time. The XRD analysis of defect structures requires the use of a well-justified underlying model that connects a certain dislocation density and distribution with a total displacement gradient field. ECCI is a scanning electron microscopy (SEM) technique that relies on the backscattered electron intensity being dependent on the orientation of the crystal lattice planes with respect to the incident electron beam due to the electron channeling mechanism. Slight local distortions in the crystal lattice due to dislocations cause a modulation of the backscattered electron intensity, allowing the defect to be imaged. However, like other techniques, the ECCI methods are slow and not ready for production inspection. Two-dimensional CL images may be used to deduce the dislocation densities of the films. CL measurements may be performed at room temperature by using a field emission scanning electron microscope with electron beam energy of 10 keV. The spatial localization of the emission energy is unambiguously determined by measurements of the spatially-resolved monochromatic CL. Since the dislocations should not emit any luminescence, the positions corresponding to dislocations in the epitaxial film are relatively dark in the CL image. However, for CL to be effective in a “nondestructive” mode, low beam power is required.